The present invention relates to a core sampler system for taking out samples from loads of granular material and of the type comprising a tubular sampling spear for introduction into selected areas of the material load. Samples are taken, inter alia, for measuring the degree of purity of a charge of material such as grain, seed, beans or other granular material carried by a ship or a truck, e.g. in connection with a truck being placed on a weighbridge, and hereby it is of course crucial that the samples be fully representative of the material. This may contain both relatively heavy and relatively light impurities, and by the introduction of a simple tubular spear the impurities may easily be deplaced in such a manner that they are not received by the spear in exactly the proportions in which they occur in the granular material. Normally there are only a few per cent of impurities in the material, i.e. the samples should ideally be taken with an extreme accuracy to ensure a representative distibution of the impurities in the samples.
It has been found long ago that samples taken by a simple introduction of a tubular sampling spear will normally be very far from being representative with respect to the impurities in the material, and great efforts have been made to improve this circumstance. Thus, it has been endeavored to achieve a certain improvement by carrying out a suction on the tubular sampling, but it has been found, however, that an associated "vacuum cleaner effect" at the insertion end of the spear has caused a suction intake of a disproportionately large amount of impurities from the surroundings of the spear tip, such that the sample result is still not fully representative. The result may even be still more inaccurate, particularly with materials having relatively large particles, e.g. beans and peas.
The most accurate results so far have been obtained by using a tubular sampling spear consisting of an inner suction pipe and a surrounding pipe for supply of pressurized air, the insertion end of this spear being embodied as a short, exteriorly tapering pipe portion, which communicates axially with the mouth of the central suction pipe through an inner ring slot area wherefrom air is conveyed into the inner mouth of the suction pipe from the surrounding pressurized air pipe. The spear is connected in a closed air circulation system in which the pressure side of the blower is connected directly to the pressurized air supply of the spear, while the suction pipe of the spear, i.e. the outlet pipe for air and grain is connected to the suction side of the blower through a grain separator. It is aimed at that the static air pressure in the ring nozzle area corresponds to the ambient pressure or is very close to this, such that adjacent the ring slot no considerable over- or subpressure will occur, which might be transmitted to the material inside and outside the end of the spear. By this system strongly improved results have been obtained, probably because the material is conveyed away from the spear end without any associated "vacuum cleaner effect" and without the material in compact form being able to penetrate into the spear further than through the short, distance from the tip to the ring nozzle area. Thus, hereby no long "plug" will be formed in the pipe, which through friction against the inner sides of the pipe might cause a noticable pressure against the material, which, by the insertion of the spear, is about to be introduced into the spear pipe, and it is presumed that by sample taking with a simple pipe spear with associated closable slots it is such a pressure build-up in front of the spear tip which, by the movement of the spear and by the opening and closing of the said closeable slots thereof, contributes to the considerable inaccuracy of the sample taking.
The invention relates to a sampling system of the abovementioned air circulation type, and its purpose is to provide such a modification of this type of system that a further improvement of the sample accuracy is obtainable, the previously obtained accuracy being relatively good, but not at all satisfactory, particularly when the impurities consist of seed weeds, sand, or soil particles. The invention is based on the consideration that a very weak suction effect could be established advantageously at the spear end, which would facilitate the material passage through the short "plug portion" between the outer spear tip and the ring slot area, such that a pressure build-up in front of the spear tip may be further reduced without any considerable or harmful vacuum cleaner effect.
According to the invention such a weak suction effect is not provided through any changed dimensioning of the system, but through the very simple measure of a small hole being provided in the wall of the air conduit on the pressure side of the blower in the closed system, preferably close to the the concerned junction between the sampling spear and an air supply hose connected thereto, and preferably a hole having an area of the magnitude 1/10 of the diameter of the suction pipe. A certain amount of air will be pressed out through this hole during the operation of the system, and as the system is otherwise closed, this air outlet must result in a corresponding suction intake effect in such a part of the system where this is possible, i.e. at the spear end as being open to the surroundings such that the desired weak suction effect is brought about in a well-defined manner just at this place. A large number of experiments have proven that with the system according to the invention it is possible to obtain a highly improved accuracy of the sample taking, even though it must be admitted that a precise explanation of this fact be given,
The optimal size of the hole will depend on the basic parameters of the air circulation system, and it can be mentioned that the hole should be of a slightly increasing size, the larger the conduit or hose connection between the blower and the spear is. Under circumstances as explained below it may even be desirable to provide a corresponding, but smaller hole in a wall portion of the suction side of the system.